With the advancement of bioelectronics, portable health monitoring devices are getting popular for they are able to provide continuous monitoring of an individual's health condition with ease of use and comfort. The portable health monitoring devices are increasingly used at places such as home, ambulance and hospital, and at situations including military training and sports.
Pulse rate and blood flow characteristics are important parameters subject to continuous monitoring because they are important in assessing the health condition of an individual. Healthcare institutes such as the hospitals and elderly care centers can use this information to remotely monitor the health conditions of their patients. This is particularly important for paraplegic patients whose blood flow anomalies need to be detected early. In addition, blood flow anomaly monitoring for patients after major surgeries is important to ensure patients' smooth recovery.
Furthermore, pulse rate and blood flow information of individuals subjected to crowded and cramped conditions with limited physical activity may be utilized to trigger alert for immediate attention when blood flow anomalies, such as deep vein thrombosis, are detected. Similar monitoring and alert system may also be deployed during disaster where life condition of the affected personnel can be assessed continuously for rescue risk management. Finally, it is important for monitoring of the pulse rate and blood flow of personnel working in dangerous environments such as deep sea condition (divers), high temperature (fire-fighters), and deep underground (coal miners).
Current apparatuses for non-invasive measurements of blood pulse rate use electrical, mechanical and optical means for sensing. The apparatuses can come in the form of chest stripes, socks attachments, wrist-watches, and finger attachments. However, each of the apparatuses for blood pulse measurement has its weaknesses. Chest stripes and sock attachments usually measure the body electrical signals to determine the pulse rate; it is simple but requires the use of complex algorithms and/or reference signals to reduce noise due to motion artifacts. Measurement of pulse rate by mechanical means employs the detection of pulsation on the skin, which is highly susceptible to other motion artifacts. Optical means for pulse rate measurements usually come as finger attachment device. Such device employs the use of special light sources and detectors, which normally results in higher power consumption. With the various apparatuses discussed above, it is important to note that most of these apparatuses are not able to acquire information on blood flow.
Another type of apparatuses for measuring pulse rate and blood flow employs non-invasive electromagnetic method. For example, U.S. Pat. No. 5,935,077 discloses an electromagnetic blood flow sensor that uses a bipolar magnetic field source to provide a varying magnetic field with a component parallel to the skin and through the blood vessel, a single sense electrode on the skin adjacent to the blood vessel, a reference electrode, and a detector that samples the sense electrode signal in synchronism to the varying magnetic field. However, the non-invasive electromagnetic apparatuses using electrodes to measure pulse rate and blood flow have poor signal-to-noise ratios as most of the systems employ electrodes; the apparatuses are more susceptible to body electrical noise and motion artifacts. In addition, most of these apparatuses employ the reversal of magnetic field polarity to achieve signal acquisition of pulse rate and blood flow information. This method usually requires the use of an electromagnet, which will result in high power consumption. As such, the current electromagnetic apparatuses of pulse rate and blood flow monitoring are not portable and are not meant for ambulatory use.
The inventors of the present invention have previously discovered a magnetic method for non-invasive detection blood pulse rate and flow anomalies without the need of direct contact between sensor and skin. See, Singapore patent application No. 200601301-5, titled “Apparatus and method for non-invasively sensing pulse rate and blood flow anomalies” which is incorporated herein for its entirety. The magnetic method has many advantages over other non-invasive methods. For example, the other non-invasive methods acquire their signals by deforming the blood vessels. The deformation of blood vessels could be achieved by for example the use of a gaseous device as disclosed in U.S. Pat. App. No. 2004/0010199 A1. In contrast, the magnetic method does not need any deformation of blood vessels for signal acquisition.